1. Field of the Invention
This non-provisional application claims the benefit of Patent Cooperation Treaty (PCT) International Application No. JP96/02446, filed Aug. 30, 1996.
This invention relates to an image display device such as an active matrix liquid crystal display device, an image display method, and a display drive device, together with electronic equipment using the same. More specifically, it relates to an improvement in the operation of writing data that can reduce the occurrence of ghosting.
2. Description of Related Art
In an active matrix type of liquid crystal display device, for example, an operation of writing data to a liquid crystal layer of each of a number of pixels is implemented by a point-at-a-time scanning, through a switching element that is a thin-film transistor (TFT), where a plurality of these TFTs are connected to a single scan signal line.
However, to answer the recent demands for a device capable of handling multi-media data, such as a personal computer (PC) or engineering workstation (EWS), it is desirable to provide a display having a lot of gray levels such as 256 gray levels when displaying a natural-seeming image such as a video signal.
To adapt a prior-art digital driver to cope with this large number of gray levels, it is necessary to have a number of input signals for each color that is equal to the number of bits. For a color display of 256 gray levels, for example, the number of input signals is: 3 (R, G, and B).times.8 bits=24 input signals.
With an analog driver, on the other hand, three input signals are sufficient for a color display or one for a monochrome display. In contrast to a digital driver that has discontinuous gray levels, an analog driver has continuous gray levels which gives it the advantage that it is suitable for a display that is based on a normal image signal.
Unfortunately, it is necessary to sample and hold data from within an image signal in components such as TFT switches, in order to achieve the above point-at-a-time scanning in an active matrix type of liquid crystal display device. This gives rise to a problem in that the switching characteristic of the TFT cannot follow the frequency of the input image signal fast enough. In a display device with an integral driver, the capabilities of sample-and-hold TFTs is lower than in a display device with an external driver, and thus this problem is more obvious. With a high-definition display device having a large number of pixels, the frequency of the input image signal is higher, so this problem is more obvious.
Therefore, a technique has been proposed (in Japanese Patent Application No. 6-316988) whereby the input picture signal is phase-expanded to, for example, six parallel signals as shown in FIG. 32, to increase the time length of data per pixel and reduce the frequency of the signal input to the liquid crystal panel.
This phase expansion makes it possible to increase the time length of data for each pixel and increase the resolution, even with the frequency characteristics of a TFT used as, for example, a sample-and-hold switch.
FIG. 32 shows how the time length of data for each of the phase-expanded signals that are output in parallel after the 6-phase expansion has a time length that is equal to six cycles of a reference clock signal.
When these phase-expanded signals are sampled by the sample-and-hold switch such as a TFT, the sampling period of a sampling signal that is input to the gate of the TFT, for example, is set to eight cycles of the reference clock signal, as shown in FIG. 32, as a test.
This setting is a sufficiently long sampling period with respect to the time length of data in the phase-expande signals, from consideration of the frequency following characteristics of a TFT switch. It also means that a sampling signal having this sampling period can be created easily by using a shift register alone.
However, experiments performed by the present inventors have shown that, when an attempt is made to display an arrow 1 on a screen 2, as shown schematically in FIG. 33 for example, ghosting 3 can occur in subsequent positions of travel in the scan direction, as shown by the broken line.
An objective of this invention is thus to provide an image display device, image display method, and display drive device that make it possible to reduce or prevent ghosting, even while an input image signal is being subjected to phase expansion, as well as electronic equipment that uses the same.
Another objective of this invention is to provide an image display device, image display method, and display drive device that make it possible to reduce or prevent ghosting, even when increasing speed of the dot clock signal makes it no longer possible to follow the sample-and-hold operation during the point-at-a-time scanning, as well as electronic equipment that uses that method.